Rift Valley Fever (RVF) is a viral disease endemic to sub-Saharan Africa and has been the cause of several recent epizootics and epidemics in Egypt. It is a mosquito-borne enveloped RNA virus, also infectious via the aerosol route. Following a 2-6 day incubation, it typically causes acute febrile illness, and about 10% of those develop retinitis, 1% blindness, and about 1% develop a fulminant course with up to 50% mortality. RVF virus is a class A high priority bioterrorism agent. It has the potential to amplify and be transmitted by many mosquito species found in the United States. Prior vaccination efforts in humans have included an IND formalin inactivated vaccine. It produced neutralizing antibodies but it required a three-shot primary series and repeated boosters. To enhance immunogenicity, USAMRIID created a live vaccine designated MP12, which was mutagenized and attenuated by serial passage in the presence of 5-fluorouracil with subsequent plaque cloning and amplification. Approximately 60 volunteers were immunized under an IND prepared in the early 1980's. Results were promising in that protective antibodies were formed following one injection, and these remained after one year. Minimal side effects were observed. This vaccine has since been considered a prime candidate for a licensed RVF vaccine. This project will continue this vaccine development by comparing the attenuated vaccine with the parent using DNA sequencing to precisely identify the mutation points and provide a basis to quantitatively determine the genetic stability of the attenuated virus at the DNA sequence level. Several volunteers vaccinated under the present IND will be inoculated, and we will examine recovered virus for any signs of reversion again by DNA sequence analysis. We will determine the growth conditions in an optimized host cell line, establish a master cell bank and viral seed lot to be used for further production, and write a new IND to support final phase II and III clinical testing of the vaccine. [unreadable] [unreadable]